One of the most significant engineering problems which must be overcome in the development of an internal combustion engine, such as a gasoline or diesel engine, is the suppression of engine "knock".
As is well known, knocking is generally caused when the crankshaft journal is aligned with the piston rod, so that the piston is essentially at its maximum position of compression in the cylinder, which is known as the "top dead center" position. Upon ignition, the compressed, vaporized fuel within the cylinder may fire too rapidly, rather than burn with a smooth combustion rate. This explosive combustion creates a shock wave which strikes the piston, placing tremendous stress upon the piston, the piston rod, and the crankshaft.
Because of this problem, pistons and piston rods must be designed to endure a level of shock which is not customarily encountered during normal operation of the engine. Also, because of this problem, lead fuel additives or high test gasoline are often required, which adds to the fuel expense. Furthermore, high test gasoline, although more expensive, actually carries less available energy per gram than the more violently burning low test gasoline.
Furthermore, because of the need to avoid the damaging effects of engine knock, the maximum compression in the cylinder must often be reduced, to avoid preignition. Also, at lower engine speeds the spark plugs are usually set to fire after the piston has passed the top dead center position, i.e. after the piston has begun its withdrawal from the cylinder. This is desirable from the point of view of avoiding damage from knocking, since any shock that is transmitted to the piston can then be transmitted to the rotating crankshaft. Such is not the case at the precise top dead center position or before in conventional piston-crankshaft arrangements, since at the top dead center position, force cannot be transmitted from the piston and piston rod into the crankshaft in the form of torque, because at that moment the crankshaft journal is aligned with the piston rod.
As a further technique of avoiding the undesirable effects of engine knock, the cylinders of the conventional internal combustion engine are designed to be smaller than they might otherwise desirably be, with large numbers of cylinders provided. Accordingly, the major United States auto manufacturers have provided their customers with six and eight cylinder engine automobiles, in which each cylinder has a displacement volume of, for example, 800 cubic centimeters.
Furthermore, as another means for reducing the undesirable effects of engine knock, engines are set to run rapidly at a high number of revolutions per minute, for example a typical cruising rate of 3,000 r.p.m.
Many of the above conventional and commercial engine characteristics are in themselves undesirable, but have been accepted by the industry in order to minimize the bad effects of engine knock, which can damage the piston and piston rods of an improperly designed engine. For example, if combustion in the cylinders could be safely initiated while the piston was in top dead center position, a substantial increase in the efficiency of the engine would result. In the present commercial designs, the amount of the travel of the piston from top dead center to the retracted position at which the spark plugs are fired is completely wasted, in terms of obtaining power from the engine.
Also, a greater efficiency can be obtained with a higher compression of the air-fuel mixture before firing.
Similarly, but for the problem of engine knock and lugging, an engine having a few large cylinders operating at a low number of revolutions per minute could be quite attractive. A large cylinder can be very powerful, and, especially when operating at a low r.p.m. rate, would have a distinct tendency to provide more complete burning of the exhaust gases, resulting in a lower hydrocarbon emission, even without the use of anti-pollution equipment. Oxides of nitrogen tend to be formed next to the cylinder wall, and complete burning can be inhibited there. A large cylinder has less wall surface area for its working volume. Thus, use of a larger cylinder will result in proportionately less undesirable exhaust components.
Because of the capability of the engine disclosed herein to operate at low rates (revolutions per minute), the usual problems of engine balance and lack of smoothness associated with engines having few cylinders can be greatly reduced.
Similarly, the fact that an engine operates at a lower number of revolutions per minute (r.p.m.) results in more complete burning and in a greater and more efficient utilization of the energy which is released, plus a reduced hydrocarbon emission, and longer engine life.
However, the full realization of the above advantages has not been achieved in the prior art because of the tremendously damaging effects of engine knock and the lack of efficient operation at lower r.p.m. rates. Previously, the avoidance of these two problems has required the designing of fast engines, having many small cylinders, in which the firing of the cylinders is set after top dead center position, and in which the maximum fuel-air mixture compression before firing has been restricted. The problems created by these solutions, such as high wear factors, high r.p.m. stress factors, higher cost, etc. have been deemed preferable to the problems they are designed to eliminate.
Numerous attempts are reported in the patent literature to dispense with the problem of engine knock; see, for example, the following U.S. patents: Anderson Pat. No. 2,134,995; Goodwin Pat. No. 1,752,379; Bugatti Pat. No. 2,151,835; Mallory Pat. No. 1,379,115; and Vriend Pat. No. 3,574,293. None of the structures of the above-cited patents appears to have come into significant commercial use, apparently because of their undesirable complexity in some instances, and in other cases because of their primary reliance upon springs, rubber bushings, and the like, which are generally incapable of providing reliable, long-term performance.
The invention of this applciation provides a simple, reliable apparatus for obtaining the above-described advantages by shock mounting an engine, cushioning it from the effects of shock caused by knocking, or "lugging", which can result from operation at undesirably low speed under too heavy a load or too high a gear ratio. Accordingly, the engine can be designed for greater efficiency, with less concern about the effects of knocking and lugging.
The apparatus of this invention can be expected to have a life span which corresponds to the rest of the engine, and yet is simple, self-contained, completely automatic, and requires structural modifications differing greatly only at the crankshaft and piston rod from that which is customary and conventional in the present internal combustion art.
As a further advantage, while the pistons of this engine are shock mounted during the combustion cycle in an engine to protect against engine knock and lugging, the shock mounting feature may be spontaneously deactivated during the piston compression cycle, so that the piston advances into the cylinder to a precisely predetermined point, unimpeded by any "play" in the piston rod or the like. Accordingly, a precise spacing of the piston in the cylinder can be achieved at top dead center to obtain the desired compression, but also, the desired advantages described above can be achieved.
Also, the immediate displacement of the piston upon detonation permitted by this invention can result in a quicker release of combustive pressures, resulting in a lower operating temperature.